1. Field of the Invention
The present invention relates to the piezo-electric actuator of the print head of an ink jet printer and a method for producing such an actuator.
2. Description of Related Art
The print head of a known ink jet printer has ink channels and piezo-electric elements provided adjacently to them. The ink jet printer performs printing a print by applying a voltage to the piezo-electric elements to reduce the volume of one or more of the ink channels, ejecting ink from this channel or these channels through an orifice or orifices.
FIG. 11 of the accompanying drawings shows the print head of a conventional ink jet printer, which is disclosed in the Assignee""s U.S. Pat. No. 5,402,159, for example. This print head includes a piezo-electric actuator 103, which is provided over ink ejectors 90a, 90b and 90c. The piezo-electric actuator 103 includes five piezo-electric ceramic sheets or layers 40 laminated or stacked together. An internal negative electrode 42 lies on the upper side of each of the top, middle and bottom ceramic sheets 40. Separate internal positive electrodes 44a, 44b and 44c lie on the upper side of each of the other two ceramic sheets 40. The positive electrodes 44a, 44b and 44c are provided over or above the ink ejectors 90a, 90b and 90c, respectively. The ink ejectors 90a, 90b and 90c have ink channels 32a, 32b and 32c, respectively, and orifices 37a, 37b and 37c, respectively. This print head consists of a small number of parts and is simple in structure. It is easy to make the resolution of the print head higher by varying the electrode pattern. The use of the laminated piezo-electric actuator 103 results in lower drive voltage.
A deformation restraining member 80 is bonded to restrain the piezo-electric actuator 103 from deforming away from the ink channels 32a-32c. This makes it possible to deform the piezo-electric actuator 103 effectively toward the ink channels 32a-32c and consequently drive the ink ejectors 90a-90c at lower voltage. This also makes it possible to reduce the cross talk at each ink channel 32a, 32b or 32c which is caused by the deformation of the adjacent ink channel or channels due to irregular deformation of the piezo-electric actuator 103. The cross talk reduction improves the SN ratio (S/N).
The process for producing this print head includes alternately stacking, pressing and calcining the piezo-electric ceramic sheets 40 and the internal electrodes 42 and 44a-44c, and thereafter bonding the deformation restraining member 80 with an adhesive or the like. This complicates the process, increases the number of steps of the process, and raises the production cost.
In view of the foregoing problems, it is an object of the present invention to provide a piezo-electric actuator for an ink jet printer head which makes it possible to reduce cross talk, restrain the laminated piezo-electric element of the print head from deforming away from the ink channels of the head, and which can be assembled simply and produced at a low cost. It is another object to provide a method for producing such an actuator.
In accordance with a first aspect of the present invention, a piezo-electric actuator is provided for an ink jet printer head which has an ink channel and an orifice, and which ejects ink from the channel through the orifice by changing the volume of the channel. The actuator includes an active layer and a restraining layer. One side of the active layer faces the ink channel. The active layer includes at least one sheet formed out of piezo-electric material and provided with an electrode thereon. The restraining layer is positioned on the other side of the active layer, and restrains the active layer from deforming. The restraining layer includes at least one sheet. The active and restraining layers are sintered to be integral with each other.
The active layer is interposed between the ink channel and the restraining layer, which is formed integrally with the active layer. The restraining layer restrains the active layer from deforming. This makes it possible to efficiently utilize the deformation of the active layer to change the volume of the ink channel. It is therefore possible to improve the ink ejecting performance of the print head and reduce power consumption. This also makes it possible to prevent deformation in parallel to the layers to restrain the volume change of the ink channel or channels adjacent to a driven ink channel. It is therefore possible to prevent cross talk.
The active and restraining layers are formed by being integrally sintered. Consequently, in comparison with the case where a deformation restraining member is bonded with an adhesive or the like, it is possible to reduce the number of steps of the process for producing the piezo-electric actuator. This simplifies the producing process and lowers the production cost. It is also possible to increases the strength of the actuator.
The sheets of the active and restraining layers may be formed out of the same material. In this case, members for forming the active layer can be used as they are for the restraining layer. This makes it possible to produce the piezo-electric actuator simply at a lower cost. The same material makes the layers fit together, and prevents them from being warped, distorted or deformed, when they are integrally sintered. This results in high accuracy or precision.
The sheet of the restraining layer may be provided with a dummy electrode, which does not contribute to the deformation for driving the ink channel. In this case, when the active and restraining layers are integrally sintered, it is possible to equalize the differences in shrinking percentage in the directions perpendicular to the layers to prevent warps and/or waves due to the difference in shrinking percentage between the layers. This can made the piezo-electric actuator very flat. Consequently, the actuator can be bonded closely to the cavity layer in which the ink channel is formed. This results in high accuracy or precision.
The dummy electrode of the restraining layer may be connected to the electrode of the active layer, and face this electrode through a ceramic, which is a dielectric. In this case, there is no potential difference between the dummy electrode and the electrode of the active layer, producing no electric capacity between them. As a result, no electric power is wasted.
The dummy electrode of the restraining layer and the electrode of the active layer may be positioned in substantial symmetry in the piezo-electric actuator. In this case, when the active and restraining layers are integrally sintered, it is possible to roughly equalize the differences in shrinking percentage in the directions perpendicular to the layers to prevent warps and/or waves due to the difference in shrinking percentage between the layers. This can make the piezo-electric actuator even flatter. Consequently, the actuator can be bonded closely to the cavity layer. This results in high accuracy or precision.
In accordance with a second aspect of the present invention, a piezo-electric actuator is provided for an ink jet printer head. The actuator includes a laminate including a plurality of piezo-electric sheets stacked and sintered at the same time. The actuator also includes an electrode formed on at least one of the sheets which is positioned on one side of the laminate. Only said at least one sheet on the one side is adapted for activation with a drive voltage. At least one of the sheets which is positioned on the other side of the laminate is not adapted for activation (deactivated). This actuator is simple in structure and therefore very easy to produce.
In accordance with a third aspect of the present invention, a print head is provided for an ink jet printer. This print head includes an ink ejector having an ink channel formed therein and an orifice through which ink can be ejected from the channel. The print head also includes a piezo-electric actuator for changing the volume of the ink channel. The actuator includes an active layer and a restraining layer. One side of the active layer faces the ink channel. The active layer includes at least one sheet formed out of piezo-electric material and provided with an electrode thereon. The restraining layer is positioned on the other side of the active layer, and restrains the active layer from deforming. The restraining layer includes at least one sheet. The active and restraining layers are sintered to be integral with each other. The print head includes a piezo-electric actuator according to the invention, and is therefore highly reliable and low-cost.
In accordance with a fourth aspect of the present invention, a method is provided for producing a piezo-electric actuator for an ink jet printer head. The method comprises the steps of:
providing at least one first green sheet having an electrode pattern, the first green sheet being formed out of piezo-electric material and forming an active layer of the actuator;
laying at least one second green sheet on the first green sheet, the second green sheet forming a restraining layer of the actuator; and
calcining the first and second green sheets at the same time to be integral with each other.
This producing method involves forming the active layer and the restraining layer by calcining them. The restraining layer restrains the active layer from deforming away from the ink channels of the print head. It is therefore possible to efficiently utilize the deformation of the active layer to change the volume of the ink channels. This makes it possible to improve the ink ejecting performance of the print head and reduce power consumption. It is also possible to prevent the horizontal or lateral deformation of the active layer to restrain the volume change of the ink channel or channels adjacent to a driven ink channel, preventing cross talk. In particular, the active and restraining layers are formed by being integrally sintered. Accordingly, in comparison with the case where a deformation restraining member is stuck with an adhesive or the like, the piezo-electric actuator can be produced at a low cost by a simple process including a reduced number of steps, and its strength can be high.
The second green sheet, too, may be formed out of the piezo-electric material. A plurality of first green sheets and a plurality of second green sheets may be provided. The producing method may further comprise the step of providing at least part of the second green sheets with a dummy electrode or dummy electrodes. The second green sheets may include a sheet provided with a dummy electrode and a sheet provided with no dummy electrode. In this case, the restraining layer includes a sheet provided with a dummy electrode, which does not contribute to deformation, and a sheet provided with no dummy electrode. Therefore, when the active and restraining layers are integrally sintered, it is possible to equalize in balance the differences in shrinking percentage in the directions perpendicular to the layers to prevent warps and/or waves due to the difference in shrinking percentage between the layers. This can made the piezo-electric actuator very flat.
The second green sheet without a dummy electrode may be laid on the second green sheet provided with a dummy electrode. In this case, the restraining layer includes a sheet having no dummy electrode and laid on a sheet provided with a dummy electrode, which does not contribute to deformation. Therefore, when the active and restraining layers are integrally sintered, the dummy electrode can restrain the electrode pattern on the active layer from diffusing, and it is possible to equalize in balance the differences in shrinking percentage to prevent warps, making the piezo-electric actuator very flat.
The producing method may further comprise the steps of pressing with heat and then degreasing the first and second green sheets before calcining them.